Hello everyone,
I heard when define a struct, it is important to make the size of the struct memory aligned.
For example,
Code:struct foo { char p; char[3] align; };struct foo is better than struct goo, even if we only use member p.Code:struct goo { char p; };
Allocate 3 bytes to align with memory. But I do not know why make memory aligned is better. Any reasons? (for example, prevent memory from running out?)
thanks in advance,
George
Then look into your compiler's documentation of how to assure memory alignment. Such things are non-standard.Originally Posted by George2
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
The computer has to retrieve memory starting at a word-aligned address. Modern compilers automagically do this alignment for you unless you specifically give the compiler-specific preprocessor directive to pack it. On some architectures it can actually create a SIGBUS error if your structure isn't word-aligned.
Feel free to correct any mistakes I've made in the above statements. I think everything is accurate but I'm not 100% sure.
If you understand what you're doing, you're not learning anything.
> struct foo is better than struct goo, even if we only use member p.
Not so.
Manually aligning structures is a waste of time. The compiler will do it for you if it's necessary to do it, and it will do it with the right number of bytes.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Check out some of these hits: http://www.google.ca/search?hl=en&q=...+padding&meta=
Especially the Wikipedia entry: http://en.wikipedia.org/wiki/Data_structure_alignment
dwk
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